Figure legends
Figure 1 Characterization of the studies included based on outer or inner layer biodiversity.
Figure 2 Forest plot for the association between Shannon diversity index and asthma.
Figure 3 Forest plot for the association between bacterial richness and asthma.
Figure 4 Forest plot for the standardized mean difference of the Shannon diversity index among individuals with and without asthma.
Figure 5 Forest plot for the standardized mean difference of the bacterial richness among individuals with and without asthma.
Figure 6 Forest plot for the association between bacterial richness and asthma.